Prior knowledge is essential to learning. In fact, the process of learning can be thought of as what one does to connect and reintegrate new understandings with existing knowledge. Prior knowledge includes formal learning, such as a preschool learning the rule about not crossing the street without looking both ways, but it also includes a multitude of implicit, self-taught explanations about how the world works. These intuitions or self-taught theories can sometimes facilitate new learning, as when scientific explanations are easily mastered because they “make sense” and jibe with our previous experience. Intuitive theories can also be the source of serious misconceptions that hinder new learning and are relatively impervious to instructional change unless students are given a structured way to work through the inconsistencies between their intuitions and contradictory evidence.